Conventionally, a rotating field type synchronous motor (hereinafter referred to as an IPM motor) with a structure where permanent magnets are embedded inside a rotor is known as a rotary electric machine mounted and used in a vehicle.
Since the IPM motor is highly efficient because it is possible to utilize both reluctance torque due to the magnetization of the rotor and torque due to the magnetization of the permanent magnet, the IPM motor is preferably employed in a hybrid vehicle or an electric vehicle.
Such an IPM motor includes a stator that functions as an armature, and a rotor that functions as a magnetic field disposed to face the stator in a radial direction.
A rotor equipped with a shaft (rotation axis) having knurled portions formed by knurl processing on an outer peripheral surface thereof, and a rotor core having a fitting-recess that is fitted and fixed to the knurled portions of the shaft are disclosed in Japanese Patent Application Laid-Open Publication No. 2-294241.
Incidentally, in the above IPM motor, the rotor core generates heat due to a core loss of the rotor core and eddy current loss by the permanent magnets.
However, as the rotor disclosed in the above Publication '241, when the knurled portion of the shaft is fitted into the fitting-recess of the rotor core by press-fitting, the shaft and the rotor core are in contact only at tips of the knurled portion.
Therefore, since the heat of the rotor core is transmitted to the shaft through air in gaps formed between the knurled portions of the shaft, and an internal wall of the fitting-recess of the rotor core, heat radiation properties are low.
If the heat radiation properties of the rotor core are low, it causes demagnetization of magnets, lowering strength of secondary conductors, or seizure of bearings.
Moreover, when an engagement in the knurled portion is enlarged in order to increase contacting areas between the shaft and the rotor core, it is necessary to increase the press-fitting force of the shaft into the fitting-recess of the rotor core, thus the productivity may become worse.